Cost Basis

Full explanation

Cost basis is the original value of an asset for tax purposes — usually what you paid for it, plus commissions and fees. When you sell the asset, your capital gain (or loss) is the difference between the sale price and the cost basis. For stocks, basis is typically the purchase price. For inherited property, basis is usually the fair market value at the date of death (stepped-up basis). For crypto, basis is the purchase price in USD at the time of acquisition. Tracking cost basis accurately is critical for correct tax reporting.

Source: IRS Publication 551 — Basis of Assets